Magnetic proppants for enhanced fracturing

ABSTRACT

The present application relates to compositions and methods for enhancing fracturing operation. In some embodiments, the present application includes compositions and methods that are used to minimize clustering of proppants or introduce proppants into narrow fractures. In some embodiments, the compositions and methods involve magnetic proppants.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/170,560, filed Oct. 25, 2018, which claims the benefit of U.S.Provisional Patent Application No. 62/615,059, filed Jan. 9, 2018, thecontents of which are hereby incorporated by reference herein in theirentireties.

FIELD

The present application relates generally to methods and compositionsfor enhancing a fracturing operation.

BACKGROUND

Fracturing is a method to connect a wellbore with a rock formation forgas production. The process of fracturing is conducted by pumpingfracking fluids at a flow rate exceeding the breaking pressure of therock formation to create fractures. Traditionally, the fracking fluidscarry solid materials known as proppants, which serve to keep thefractures open after fracturing the rock formation and to improveconnectivity with the wellbore. If these proppants are not included, thefractures tend to close up, blocking the flow from the rock formation tothe wellbore.

SUMMARY

The present application stems in part from the realization that currentproppants do not always reach into all the fractures due to the geometryand size of the proppants as illustrated in FIG. 1. Because of theselimitations, proppants can cluster and accumulate at certain locationswithin the fracture network, bridging and blocking other proppants fromreaching into the deepest fractures as depicted in FIG. 1.

The present application provides strategies for enhancing fracturingoperation. Embodiments of the present application include compositionsand methods that can be used to minimize clustering of proppants orensure that proppants reach into the deepest fractures and therebyenhance fracturing operation. In some embodiments, the methods andcompositions involve magnetic proppants. In some embodiments, themethods and compositions utilize proppants with various sizes ordensities, or both. Among other things, the present applicationencompasses the identification of the source of a problem whenconventional proppants are used for the fracturing process.

In one aspect, the present application relates to methods for enhancinga fracturing operation in a rock formation. The methods includeintroducing a fracking fluid comprising magnetic proppants into a rockformation, wherein a median diameter of the magnetic proppants in thefracking fluid introduced into the rock formation increases over time.

In some embodiments, the method comprises introducing sequential batchesof fracking fluid into the rock formation and the median diameter of themagnetic proppants in the fracking fluid increases in a step-wisefashion from batch-to-batch. In some embodiments, the method comprisesadding sequential batches of magnetic proppants to a continuous streamof fracking fluid that is introduced into the rock formation, whereinthe median diameter of the magnetic proppants that are added to thefracking fluid increases in a step-wise fashion from batch-to-batch.

In some embodiments, the method comprises adding magnetic proppants to acontinuous stream of fracking fluid that is introduced into the rockformation, wherein the median diameter of the magnetic proppants thatare added to the fracking fluid increases over time.

In some embodiments, the method comprises introducing a firstcomposition comprising first magnetic proppants and a fracking fluidinto the rock formation and then introducing a second compositioncomprising second magnetic proppants and a fracking fluid into the rockformation, wherein a median diameter of the first magnetic proppants isless than a median diameter of the second magnetic proppants. In someembodiments, the method further comprises introducing a thirdcomposition comprising third magnetic proppants and a fracking fluid tothe rock formation, wherein the median diameter of the second magneticproppants is less than a median diameter of the third magneticproppants.

In some embodiments, the magnetic proppants comprise a magnetic core, aninsulator coating layer, and an outer coating layer. In someembodiments, the magnetic core comprises a first magnetic pole and asecond magnetic pole. In some embodiments, the magnetic core comprises amaterial selected from the group consisting of Co, Fe, Fe₂O₃, FeOFe₂O₃,NiOFe₂O, CuOFe₂O₃, MgOFe₂O₃, MnBi, Ni, MnSb, MnOFe₂O₃, Y₃Fe₅O₁₂, CrO₂,MnAs, Gd, Tb, Dy, EuO, and combinations thereof.

In some embodiments, the insulator coating layer is located on at leasta portion of an external surface of the magnetic core, the insulatorcoating layer comprises a material with a high magnetic permeability,and the insulator coating layer shields at least a portion of a magneticfield generated by the first magnetic pole. In some embodiments, theinsulator coating layer comprises a mu metal.

In some embodiments, the outer coating layer covers at least a portionof an external surface of the magnetic core. In some embodiments, theouter coating layer comprises a material with a high magneticpermeability embedded in a matrix material that is soluble at about 70to 300 degree Fahrenheit in a fracking fluid having a pH in a range ofabout 6 to 8. In some embodiments, the outer coating layer shields atleast a portion of a magnetic field generated by the second magneticpole. In some embodiments, the outer coating layer comprises a mu metal.In some embodiments, the outer coating layer is located on both theinsulator coating layer and the external surface of the magnetic core.In some embodiments, a diameter of the magnetic core is about 50 to 90%of a diameter of the magnetic proppant. In some embodiments, a thicknessof the insulator coating layer is about 5 to 25% of the diameter of themagnetic proppant. In some embodiments, a thickness of the outer coatinglayer is about 5 to 25% of the diameter of the magnetic proppant.

In some embodiments, the magnetic proppant further comprises aradioactive tracer.

In some embodiments, the median diameter of the first magnetic proppantsis within a range from 0.1 to 1 mm. In some embodiments, the mediandiameter of the second magnetic proppants is within a range from 0.5 to1.5 mm. In some embodiments, the median diameter of the third magneticproppants is within a range from 1 to 5 mm.

In some embodiments, the first composition has a concentration of thefirst magnetic proppants in a range of 0.1 to 20 pound per gallon. Insome embodiments, second composition has a concentration of the secondmagnetic proppants in a range of 0.1 to 20 pound per gallon. In someembodiments, the third composition has a concentration of the thirdmagnetic proppants in a range of 0.1 to 20 pound per gallon.

In another aspect, the present application relates to magneticproppants. In some embodiments, the magnetic proppant comprises (a) amagnetic core comprising a first magnetic pole and a second magneticpole, (b) an insulator coating layer located on at least a portion of anexternal surface of the magnetic core, wherein the insulator coatinglayer comprises a material with a high magnetic permeability, and theinsulator coating layer shields at least a portion of a magnetic fieldgenerated by the first magnetic pole, and (c) an outer coating layerlocated on at least a portion of the external surface of the magneticcore, wherein the outer coating layer comprises a material with a highmagnetic permeability embedded in a matrix material that is soluble atabout 70 to 300 degree Fahrenheit in a fracking fluid having a pH in arange of about 6 to 8, and wherein the outer coating layer shields atleast a portion of a magnetic field generated by the second magneticpole. In some embodiments, the magnetic core comprises a materialselected from the group consisting of Co, Fe, Fe₂O₃, FeOFe₂O₃, NiOFe₂O,CuOFe₂O₃, MgOFe₂O₃, MnBi, Ni, MnSb, MnOFe₂O₃, Y₃Fe₅O₁₂, CrO₂, MnAs, Gd,Tb, Dy, EuO, and combinations thereof. In some embodiments, theinsulator coating layer comprises a mu metal. In some embodiments, theouter coating layer comprises a mu metal. In some embodiments, the outercoating layer is located on both the insulator coating layer and theexternal surface of the magnetic core. In some embodiments, a diameterof the magnetic core is about 50 to 90% of a diameter of the magneticproppant. In some embodiments, a thickness of the insulator coatinglayer is about 5 to 25% of the diameter of the magnetic proppant. Insome embodiments, a thickness of the outer coating layer is about 5 to25% of the diameter of the magnetic proppant.

In some embodiments, the magnetic proppant further comprises aradioactive tracer.

In another aspect, the present application provides compositionscomprising (i) a plurality of the magnetic proppants and (ii) a frackingfluid. In some embodiments, the plurality of the magnetic proppants ispresent in the fracking fluid in an amount that ranges from 0.1 to 20pound per gallon. In some embodiments, the fracking fluid compriseswater, polymers and additives.

BRIEF DESCRIPTION OF THE DRAWING

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention and are not intended as adefinition of the limits of the invention. For purposes of clarity, notevery component may be labeled in every drawing. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1 depicts fractures not fully filled with conventional proppantsbecause of proppant accumulation;

FIG. 2 shows proppants with different sizes and weights. Size 1proppants are the biggest and heaviest and Size 3 proppants are thesmallest and lightest;

FIG. 3 depicts proppants with different sizes and weights distributed infractures. The smallest (Size 1) proppants reach the narrowest anddeepest fractures, the medium proppants (Size 2) fill up theintermediate sections of the fractures, and the largest and heaviestproppants (Size 3) fill up the widest sections of the fractures;

FIG. 4 shows an inner structure of a magnetic proppant according to anillustrative embodiment of the present application;

FIG. 5 depicts three different sizes of magnetic proppants, each ofwhich comprises an insulator coating layer and an outer coating layer;

FIGS. 6A-6C illustrate a fracture in the presence of exemplary magneticproppants according to the present application. FIG. 6A depicts thefracture where the magnetic proppants still comprise the outer coatinglayer shielding both of the magnetic poles. FIG. 6B depicts the samefracture after the outer coating layer has dissolved, and one of themagnetic poles is revealed causing the proppants to repel each other.FIG. 6C shows how the magnetic proppants keep the fracture open whenexternal forces would otherwise cause the fracture to collapse; and

FIG. 7 illustrates an exemplary set-up of laser cladding for depositionof the insulator coating layer, the outer coating layer, or both.

DETAILED DESCRIPTION

Throughout the description, where methods are described as having,including, or comprising specific steps, or where compositions aredescribed as having, including, or comprising specific components, it iscontemplated that, additionally, there are methods according to thepresent application that consist essentially of, or consist of, therecited processing steps, and that there are compositions of the presentapplication that consist essentially of, or consist of, the recitedcomponents.

It should be understood that the order of steps or order for performingcertain actions is immaterial so long as the method remains operable.Moreover, two or more steps or actions may be conducted simultaneously.

The present application encompasses the insight that fracturingoperation may be enhanced by using magnetic proppants of particularsizes or densities, or both that decrease clustering, or can bedelivered into deeper and narrower fractures. Furthermore, in someembodiments, the magnetic proppants may be designed so that they repeleach other within the fractures.

Magnetic Proppants

In some embodiments, magnetic proppants provided by the presentapplication comprise a magnetic core, an insulator coating layer, and anouter coating layer. An exemplary embodiment of a magnetic proppant isillustrated in FIG. 4.

Magnetic Core

In some embodiments, the magnetic core is magnetized and creates apersistent magnetic field, having a first magnetic pole and a secondmagnetic pole. In some embodiments, the magnetic core comprises one ormore ferromagnetic materials. In some embodiments, the ferromagneticmaterial is selected from the group consisting of Co, Fe, Fe₂O₃,FeOFe₂O₃, NiOFe₂O, CuOFe₂O₃, MgOFe₂O₃, MnBi, Ni, MnSb, MnOFe₂O₃,Y₃Fe₅O₁₂, CrO₂, MnAs, Gd, Tb, Dy, EuO, and combinations thereof. In someembodiments, a diameter of the magnetic core is about 0.1 to 1millimeter (mm), 0.1 to 0.5, or 0.15 to 0.4 mm. In some embodiments, adiameter of the magnetic core is about 0.1 to 3 mm, 0.1 to 1 mm, or 0.5to 1 mm. In some embodiments, a diameter of the magnetic core is about 1to 5 mm, 1 to 3.5 mm, or 1.5 to 3.5 mm.

In some embodiments, a diameter of the magnetic core is about 50 to 90%,55 to 90%, 60 to 90%, 65 to 90%, 70 to 90%, 50 to 85%, 50 to 80%, 55 to80%, 60 to 80%, or 70 to 80% of a diameter of the magnetic proppant.

Insulator Coating Layer

In some embodiments, the insulator coating layer is located on anexternal surface of the magnetic core. In some embodiments, theinsulator coating layer may not cover the entire external surface of themagnetic core. For example, the insulator coating layer covers a portionof the external surface of the magnetic core. In some embodiments, theinsulator coating layer shields a portion of the magnetic fieldgenerated by the magnetic core, so that if each of the magneticproppants comprises the magnetic core and the insulator coating layer(without the outer coating layer), the magnetic proppants repel eachother. For example, the insulator coating layer may shield the magneticfield generated by the first magnetic pole as shown in FIG. 5.

In some embodiments, the insulator coating layer comprises a materialwith a high magnetic permeability which provides a low reluctance pathfor magnetic flux. For example, the insulator coating layer may comprisea material having a magnetic relative permeability range of 10,000 to1,000,000, 50,000 to 500,000, or 50,000 to 200,000. In some embodiments,the insulator coating layer comprises a mu metal. For example, a mumetal is a nickel-iron soft magnetic alloy with very high permeability,which is used for shielding sensitive electronic equipment againststatic or low-frequency magnetic fields. In some embodiments, the mumetal is selected from the group consisting of nickel, iron, copper,chromium, molybdenum, Co-Netic, supermalloy, supermumetal, nilomag,sanbold, molybdenum permalloy, Sendust, M-1040, Hipernom, HyMu-80,Amumetal, pyrolytic graphite and combinations thereof.

In some embodiments, the insulator coating layer consists of a materialwith a high magnetic permeability (for example, a mu metal) which hasbeen deposited on a portion of the external surface of the magneticcore.

In some embodiments, the average thickness of the insulator coatinglayer is within a range of about 5 to 25%, 5 to 20%, 5 to 15%, 10 to25%, 10 to 20%, or 10 to 15% of a diameter of the magnetic proppant. Insome embodiments, the thickness may be measured from cross-sectionalimages of the magnetic proppants.

In some embodiments, the insulator coating layer covers about 15 to 85%,25 to 75%, 35 to 65%, or 45 to 55% of the external surface of themagnetic core. In some embodiments, the coverage of the insulatorcoating layer may be calculated by comparing the strength of magneticfield before and after the deposition of the insulator coating layer.

In some embodiments, the insulator coating layer may comprise anadhesive material to assist adhesion of the insulator coating layer onthe magnetic core.

Outer Coating Layer

In some embodiments, the outer coating layer covers at least a portionof the external surface of the magnetic core. In some embodiments, theouter coating layer may cover at least the external surface of themagnetic core that is not covered by the insulator coating layer. Insome embodiments, the outer coating layer may also cover at least aportion of the insulator coating layer. For example, in someembodiments, the outer coating layer may cover both the insulatorcoating layer and the external surface of the magnetic core that is notcovered by the insulator coating layer as shown in FIG. 4.

In some embodiments, the outer coating layer shields the magnetic fieldgenerated by the magnetic core that is not already shielded by theinsulator coating layer, so that magnetic proppants comprising themagnetic core, the insulator coating layer and the outer coating layerdo not repel each other. For example, the outer coating layer shieldsthe magnetic field generated by the second magnetic pole as illustratedin FIG. 4. In some embodiments, the outer coating layer facilitatespumping operations by reducing the degree of interaction (repulsion orattraction) between the magnetic proppants when they are stored andinitially added to the fracking fluid.

In some embodiments, the outer coating layer comprises a material with ahigh magnetic permeability. For example, the insulator coating layer maycomprise a material having a magnetic relative permeability range of10,000 to 1,000,000, 50,000 to 500,000, or 50,000 to 200,000. In someembodiments, the outer coating layer comprises a mu metal. In someembodiments, the mu metal is selected from the group consisting ofnickel, iron, copper, chromium, molybdenum, Co-Netic, supermalloy,supermumetal, nilomag, sanbold, molybdenum permalloy, Sendust, M-1040,Hipernom, HyMu-80, Amumetal, pyrolytic graphite and combinationsthereof. In some embodiments, the material with a high magneticpermeability (for example, a mu metal) is embedded within a matrixmaterial that is soluble at 70 to 300 degrees Fahrenheit in a frackingfluid which comprises water, polymers and additives and has a pH in therange of 6 to 8. In some embodiments, the matrix material is selectedfrom the group consisting of TervAlloy™, Elementum™, TervAlloy MMC™,Elementum™, Response™ Coatings, DissolvAssure™, SmartCORE™, andcombinations thereof.

In some embodiments, the matrix material dissolves completely within 3to 24 hours (for example, within 6 to 15 hours) after the magneticproppant is contacted with the fracking fluid at about 70 to 300 degreesFahrenheit, without stirring.

In some embodiments, the average thickness of the outer coating layer isabout 5 to 25%, 5 to 20%, 5 to 15%, 10 to 25%, 10 to 20%, or 10 to 15%of the average diameter of the magnetic proppant.

In some embodiments, the outer coating layer covers about 50 to 100%, 75to 100%, 90 to 100% or 100% of the external surface of the magneticcore.

Method of Making Magnetic Proppants

In some embodiments, a method of making a magnetic proppant comprising amagnetic core, an insulator coating layer, and an outer coating layercomprises depositing the insulator coating layer on a surface of themagnetic core. In some embodiments, the method further comprisesdepositing the outer coating layer on the surface of the magnetic coreor a surface of the insulator coating layer, or both.

In some embodiments, the method further comprises aligning the magneticcore by applying an external magnetic field, so that the insulatorcoating layer is deposited on a desired portion of the magnetic coreonly.

In some embodiments, the insulator coating layer may be chemicallydeposited on the surface of the magnetic core. In some embodiments, theinsulator coating layer may be physically deposited (for example,utilizing physical vapor) on the surface of the magnetic core.

In some embodiments, the outer coating layer may be chemically depositedon the surface of the magnetic core or the surface of the insulatorcoating layer, or both. In some embodiments, the outer coating layer maybe physically deposited (for example, utilizing physical vapor) on thesurface of the magnetic core or the surface of the insulator coatinglayer, or both.

In some embodiments, the chemical deposition method is selected from thegroup consisting of plating, chemical solution deposition,Langmuir-Blodgett method, spinning coating, dip coating, chemical vapordeposition, plasma enhanced chemical vapor deposition, atomic layerdeposition, and combinations thereof.

In some embodiments, the physical vapor may be created by thermalevaporator, electron beam evaporator, molecular beam epitaxy,sputtering, pulsed laser deposition system, cathodic arc deposition, orelectrohydrodynamic deposition.

In some embodiments, the insulator coating layer may be deposited on thesurface of the magnetic core by using laser cladding. Similarly, in someembodiments, the outer coating layer may be deposited on the surface ofthe insulator coating layer or the magnetic core by using lasercladding. For example, a material for the insulator coating layer or theouter coating layer (for example, a mu metal) can be melted andconsolidated by use of a laser in order to coat the magnetic core (orthe insulator coating layer) as illustrated in FIG. 7. The laser source(1) may provide the laser energy through the laser cutting head (2). Thelaser head may be at a short distance (for example, about 10 to 100millimeter) to the target. The deposit material (for example, theinsulator coating layer material, the outer coating layer material, themu metal) may be supplied by the powder nozzle or it can be hotwire (3).The laser head may be tilted (4) to fallow the curvature of the magneticcore (5). Without wishing to be bound by any particular theory, lasercladding may provide a permanent, strong bond. In some embodiments, themagnetic core is a commercially available permanent magnet.

Composition Comprising Magnetic Proppants

In some embodiments, compositions provided by the present applicationcomprise a fracking fluid and one or more magnetic proppants.

In some embodiments, the composition has a concentration of the magneticproppants in a range of 0.1 to 20, 0.1 to 18, 0.1 to 16, 0.1 to 14, or0.1 to 12 pound per gallon.

In some embodiments, the fracking fluid is gel, foam or liquid. In someembodiments, the fracking fluid has a pH range of 6 to 8. In someembodiments, the fracking fluid has a viscosity range of 10 to 10,000 cpat a shear rate of 10-1000 sec⁻¹.

In some embodiments, the fracking fluid comprises a solvent. Forexample, the fracking fluid comprises slick water. In some embodiments,the fracking fluid comprises one or more additives selected from thegroup consisting of a biocide, a breaker, a buffer, a clay stabilizer, adiverting agent, a fluid loss additive, a friction reducer, an ironcontroller, surfactant, a gel stabilizer, and combinations thereof. Insome embodiments, the biocide may comprise glutaraldehyde carbonate. Insome embodiments, the breaker (for example, the breaker reduces fluidviscosity) may comprise an acid, an oxidizer, or an enzyme breaker. Insome embodiments, the buffer may comprise sodium bicarbonate, or fumaricacid. In some embodiments, the clay stabilizer (for example, the claystabilizer reduces clay swelling) may comprise KCl, NHCl, or KClsubstitute. In some embodiments, the diverting agent (for example, thediverting agent diverts flow of fluid) may comprise ball sealers, rocksalt, or flake boric acid. In some embodiments, the friction reducer maycomprise an anionic copolymer. In some embodiments, the iron controller(for example, the iron controller keeps iron in solution) may compriseacetic acid or citric acid. In some embodiments, the surfactant maycomprise fluorocarbon or other non-ionic surfactant. In someembodiments, the gel stabilizer (for example, the gel stabilizer reducesthermal degradation) may comprise methanol, or sodium thiosulphate. Insome embodiments, the fracking fluid comprises carbon nanotubes.

In some embodiments, the magnetic proppants are permeable or permittiveto gas under high pressures (for example, a pressure within a range of500 to 12,000 psi). For example, in some embodiments, the magneticproppants have a gas permeability range of no less than about 1millidarcy, 0.9 millidarcy, 0.8 millidarcy, 0.7 millidarcy, 0.6millidarcy, 0.5 millidarcy, 0.4 millidarcy, 0.3 millidarcy, 0.2millidarcy, 0.1 millidarcy, 0.05 millidarcy or 0.01 millidarcy.

Magnetic Proppant Shielding Both Magnetic Poles of Magnetic Core

In some embodiments, magnetic proppants in the composition may not repelor attract each other. For example, the magnetic fields generated by themagnetic cores are shielded (for example, magnetic fields from both thefirst and second magnetic poles of the magnetic cores are shielded). Insome embodiments, the composition comprises magnetic proppants thatcomprise a magnetic core, an insulator coating layer, and an outercoating layer, as discussed above.

Magnetic Proppant Shielding One Magnetic Pole of Magnetic Core

In some embodiments, magnetic proppants in the composition may repeleach other. In some embodiments, at least a portion of the magneticfield generated by the first magnetic pole of the magnetic core, isshielded by the insulator coating layer. In some embodiments, at least aportion of the second magnetic pole of the magnetic core is exposed.

In some embodiments, the composition comprises magnetic proppants thatcomprise a magnetic core and an insulator coating layer but lack anouter coating layer, as discussed above.

In some embodiments, the composition comprises magnetic proppants thatcomprise a magnetic core, an insulator coating layer, and an outercoating layer. In some embodiments, the outer coating layer is partiallydissolved and shields only a portion of the magnetic field generated bythe second magnetic pole (for example, at least a portion of the secondmagnetic pole of the magnetic core is revealed). In some embodiments,the composition may comprise fragments of the outer coating layer thathave dissolved in the fracking fluid.

Use of Magnetic Proppants for Enhancing Fracturing Operation

In some embodiments, methods provided by the present application usemagnetic proppants to enhance fracturing operation.

In some embodiments, different sizes or weights, or both of magneticproppants are used. In some embodiments, the methods compriseintroducing a composition comprising magnetic proppants and a frackingfluid into a rock formation. In some embodiments, at least for a timeperiod, a median diameter or weight of the magnetic proppants applied tothe rock formation increases (for example, continuously or discretely,or both), as the fracking operation progresses.

In some embodiments, the methods may involve the sequential introductionof batches of fracking fluid with different magnetic proppants. (forexample a batch that includes small or light, or both magneticproppants, followed by a batch that includes medium magnetic proppants,followed by a batch that includes large or heavy, or both magneticproppants).

In some embodiments, the methods involve introducing a first compositioncomprising first magnetic proppants (for example, small or light, orboth magnetic proppants, Size 3 in FIG. 2,) followed by a secondcomposition comprising second magnetic proppants (for example, mediummagnetic proppants, Size 2 in FIG. 2). In some embodiments, a mediandiameter of the first magnetic proppants is smaller than a mediandiameter of the second magnetic proppants. In some embodiments, a medianweight of the first magnetic proppants is smaller than a median weightof the second magnetic proppants. For example, the first magneticproppants may be applied first, and then the second magnetic proppantsmay be applied second, as shown in FIG. 3. The first magnetic proppantsmay be delivered to narrower or deeper, or both fractures relative tothe second magnetic proppants. This approach may improve proppantdistribution in the fractures, and may prevent the clustering andaccumulation of proppants.

In some embodiments, the methods may involve a third compositioncomprising third magnetic proppants (for example, large or heavy, orboth magnetic proppants, Size 1 in FIG. 2). In some embodiments, amedian diameter of the second magnetic proppants is smaller than amedian diameter of the third magnetic proppants. In some embodiments, amedian weight of the second magnetic proppants is smaller than a medianweight of the third magnetic proppants. For example, the third magneticproppants may be applied after application of the first and secondmagnetic proppants, as shown in FIG. 3. The second magnetic proppantsmay be delivered to narrower or deeper, or both fractures relative tothe third magnetic proppants.

Similarly, in some embodiments, the methods may involve the applicationof fourth, fifth, sixth, seventh, eighth, ninth or tenth magneticproppants. Each application may introduce larger or heavier, or bothmagnetic proppants (for example, the median diameter or median weightmay increase as the number of the applications increases). In general,the number and characteristics of the magnetic proppants that are usedin a method of the present application will depend on the type of rockformation and the predicted fracture network. In some embodiments, thenumber and characteristics of the magnetic proppants may be selectedbased on prior data regarding the dimensions of fractures typicallyobserved or measured in the rock formation of interest (for example,based on data collected from parallel or historical fracturingoperations in the same or similar rock formations).

In some embodiments, the methods may involve the continuous introductionof a fracking fluid to which different magnetic proppants are added atdifferent time points (for example starting with the addition of smallmagnetic proppants to the fracking fluid, then adding medium magneticproppants and then adding large magnetic proppants, optionally with someperiod where both small and medium (or medium and large) proppants arebeing added to the fracking fluid to create a gradual change in themedian diameter or median weight of the magnetic proppants). It will beappreciated that the median diameter and median weight of the proppantsbeing introduced into the rock formation may change in a step wisefashion over time or may change more gradually over time (for example ina linear fashion or in accordance with a curve that can be fitted with apolynomial function).

In some embodiments, the methods may involve using magnetic proppantsthat comprise a magnetic core, an insulator coating layer, and an outercoating layer as described above. In some embodiments, during theapplication process, both magnetic poles of the magnetic cores areshielded by the insulator coating layer and the outer coating layer, sothat the magnetic proppants do not repel or attract each other. After aperiod of time, the outer coating layer dissolves in the fracking fluid,so that the magnetic proppants repel each other resulting in more stablefractures within the rock formation as illustrated in FIGS. 6A-6B.

In some embodiments, the median diameter of the first magnetic proppantsis within a range from 0.01 to 1 mm, 0.05 to 1 mm, 0.1 to 1 mm, 0.01 to1.5 mm, 0.05 to 1.5 mm, or 0.1 to 1.5 mm. In some embodiments, themedian diameter of the second magnetic proppants is within a range from0.3 to 1.5 mm, 0.3 to 2.0 mm, 0.3 to 2.5 mm, 0.3 to 3 mm, 0.5 to 1.5 mm,0.5 to 2.0 mm, 0.5 to 2.5 mm, or 0.5 to 3 mm. In some embodiments, themedian diameter of the third magnetic proppants is within a range from0.5 to 7 mm, 1 to 7 mm, 0.5 to 5 mm, or 1 to 5 mm.

Other Embodiments

Certain embodiments of the present application were described above. Itis, however, expressly noted that the present application is not limitedto those embodiments, but rather the intention is that additions andmodifications to what was expressly described in the present applicationare also included within the scope of the application. Moreover, it isto be understood that the features of the various embodiments describedin the present application were not mutually exclusive and can exist invarious combinations and permutations, even if such combinations orpermutations were not made expressly, without departing from the spiritand scope of the application. Having described certain implementationsof the methods of the present application, it will now become apparentto one of skill in the art that other implementations incorporating theconcepts of the application may be used. Therefore, the applicationshould not be limited to certain implementations, but rather should belimited only by the spirit and scope of the following claims.

I claim:
 1. A method for enhancing a fracturing operation in a rockformation, the method comprising introducing a fracking fluid comprisingmagnetic proppants into a rock formation, wherein a median diameter ofthe magnetic proppants in the fracking fluid introduced into the rockformation increases over time, wherein: each of the magnetic proppantscomprises a magnetic core, an insulator coating layer, and an outercoating layer; the magnetic core comprises a first magnetic pole and asecond magnetic pole; and the outer coating layer covers at least aportion of an external surface of the magnetic core, the outer coatinglayer comprises a material with a high magnetic permeability embedded ina matrix material that is soluble at about 70 to 300 degree Fahrenheitin a fracking fluid having a pH in a range of about 6 to 8, and theouter coating layer shields at least a portion of a magnetic fieldgenerated by the second magnetic pole.
 2. The method of claim 1, whereinthe method comprises introducing sequential batches of the frackingfluid into the rock formation and the median diameter of the magneticproppants in the fracking fluid increases in a step-wise fashion frombatch-to-batch.
 3. The method of claim 1, wherein the method comprisesadding sequential batches of magnetic proppants to a continuous streamof the fracking fluid that is introduced into the rock formation,wherein the median diameter of the magnetic proppants that are added tothe fracking fluid increases in a step-wise fashion from batch-to-batch.4. The method of claim 1, wherein the method comprises adding magneticproppants to a continuous stream of the fracking fluid that isintroduced into the rock formation, wherein the median diameter of themagnetic proppants that are added to the fracking fluid increases overtime.
 5. The method of claim 1, wherein the method comprises introducingfirst magnetic proppants into the rock formation and then introducingsecond magnetic proppants into the rock formation, wherein a mediandiameter of the first magnetic proppants is less than a median diameterof the second magnetic proppants.
 6. The method of claim 5, furthercomprising introducing third magnetic proppants to the rock formation,wherein the median diameter of the second magnetic proppants is lessthan a median diameter of the third magnetic proppants.
 7. The method ofclaim 1, wherein the magnetic core comprises a material selected fromthe group consisting of Co, Fe, Fe₂O₃, FeOFe₂O₃, NiOFe₂O, CuOFe₂O₃,MgOFe₂O₃, MnBi, Ni, MnSb, MnOFe₂O₃, Y₃Fe₅O₁₂, CrO₂, MnAs, Gd, Tb, Dy,EuO, and combinations thereof.
 8. The method of claim 1, wherein theinsulator coating layer is located on at least a portion of an externalsurface of the magnetic core, the insulator coating layer comprises amaterial with a high magnetic permeability, and the insulator coatinglayer shields at least a portion of a magnetic field generated by thefirst magnetic pole.
 9. The method of claim 1, wherein the insulatorcoating layer comprises a mu metal.
 10. The method of claim 1, whereinthe outer coating layer comprises a mu metal.
 11. The method of claim 1,wherein the outer coating layer is located on both the insulator coatinglayer and the external surface of the magnetic core.
 12. The method ofclaim 1, wherein a diameter of the magnetic core is about 50 to 90% of adiameter of the magnetic proppant.
 13. The method of claim 1, wherein athickness of the insulator coating layer is about 5 to 25% of thediameter of the magnetic proppant.
 14. The method of claim 1, wherein athickness of the outer coating layer is about 5 to 25% of the diameterof the magnetic proppant.
 15. The method of claim 1, wherein themagnetic proppant further comprises a radioactive tracer.
 16. The methodof claim 5, wherein the median diameter of the first magnetic proppantsis within a range from 0.1 to 1 mm.
 17. The method of claim 5, whereinthe median diameter of the second magnetic proppants is within a rangefrom 0.5 to 1.5 mm.
 18. The method of claim 6, wherein the mediandiameter of the third magnetic proppants is within a range from 1 to 5mm.
 19. The method of claim 6, wherein a concentration of the firstmagnetic proppants in the fracking fluid is in a range of 0.1 to 20pound per gallon, a concentration of the second magnetic proppants inthe fracking fluid is in a range of 0.1 to 20 pound per gallon, or aconcentration of the third magnetic proppants in the fracking fluid isin a range of 0.1 to 20 pound per gallon.